In the fields of wireless communication and power management, various components can be implemented using solid-state devices. For example, in radio frequency (RF) communication, the RF front-end is a generic term for the circuitry between an antenna and a digital baseband system. The RF front-end may include multiple components, such as power amplifiers, low-noise amplifiers, and voltage regulators. Such RF front-end components may include one or more semiconductor devices, such as diodes and transistors. Diodes are two-terminal devices, typically allowing the flow of current in only one direction. Semiconductor diodes come in multiple types, such as point-contact diodes, tunnel diodes, PIN diodes, and junction diodes. Junction diodes include p-n diodes and Schottky diodes. A p-n diode is formed by the junction of a p-type semiconductor (having a larger hole concentration than electron concentration) with an n-type semiconductor (having a larger electron concentration than hole concentration), thus the name p-n diode. A Schottky diode (also known as a hot carrier diode) is formed by the junction of a semiconductor with a metal or metal alloy.
There also exists multiple different semiconductor transistor devices, such as field-effect transistors (FETs). A FET is a semiconductor device that includes three terminals: a gate, a source, and a drain. A FET uses an electric field applied by the gate to control the electrical conductivity of a channel through which charge carriers (e.g., electrons or holes) flow from the source to the drain. In instances where the charge carriers are electrons, the FET is referred to as an n-channel device, and in instances where the charge carriers are holes, the FET is referred to as a p-channel device. Some FETs have a fourth terminal called the body or substrate, which can be used to bias the transistor. A metal-oxide-semiconductor FET (MOSFET) is configured with an insulator between the gate and the body of the transistor, and MOSFETs are commonly used for amplifying or switching electronic signals. In some cases, MOSFETs include sidewall spacers (or so-called gate spacers) on either side of the gate that can help determine the channel length and can help with replacement gate processes, for example. Complementary MOS (CMOS) structures use a combination of p-channel MOSFET (PMOS) and n-channel MOSFET (NMOS) to implement logic gates and other digital circuits.
These and other features of the present embodiments will be understood better by reading the following detailed description, taken together with the figures herein described. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. Furthermore, as will be appreciated, the figures are not necessarily drawn to scale or intended to limit the described embodiments to the specific configurations shown. For instance, while some figures generally indicate straight lines, right angles, and smooth surfaces, an actual implementation of the disclosed techniques may have less than perfect straight lines and right angles, and some features may have surface topography or otherwise be non-smooth, given real-world limitations of fabrication processes. Further still, some of the features in the drawings may include a patterned and/or shaded fill, which is primarily provided to assist in visually differentiating the different features. In short, the figures are provided merely to show example structures.